This invention relates to an improved process for the microbiological degradation of sterol side chains to a 17-keto group.
It is known that numerous microorganisms, for example, those of the genera Arthrobacter, Brevibacterium, Microbacterium, Protaminobacter, Bacillus, Nocardia, Streptomyces, and particularly Mycobacterium, can degrade the side chain of zoosterols and phytosterols. However, the degradation of the sterols continues to carbon dioxide and water, with 4-androstene-3,17-dione and 1,4-androstadiene-3,17-dione being formed only as intermediary products.
Since numerous zoosterols and phytosterols, e.g., cholesterol, stigmasterol, campesterol, brassicasterol and the sitosterols, are common in nature and accordingly are readily available starting materials for the synthesis of pharmacologically active steroids, numerous investigations have been conducted to control the degradation of the sterols so that during the fermentation a further degradation of the intermediately formed 4-androstene-3,17-dione and of the 1,4-androstadiene-3,17-dione is prevented.
Thus, it has been found possible, for example, to prevent the further degradation of 1,4-androstadiene-3,17-dione and 4-androstene-3,17-dione by adding inhibitors to the fermentation batches. See German Unexamined Laid-Open Applications DOS No. 1,543,269 and No. 1,593,327, as well as U.S. Pat. No. 1,208,078. By the use of inhibitors, however, conducting these reactions on a commercial scale becomes very expensive, due in part to the fact that the inhibitors employed must be removed from the fermentation cultures after the reaction has taken place, in order to avoid discharge of these materials into the waste-waters. Moreover, these conventional reactions have the disadvantage that during such processes the products in all cases are 1,4-androstadiene-3,17-dione or a mixture thereof and 4-androstene-3,17-dione and 1,4-androstadiene-3,17-dione is relatively unsuitable as a starting compound for the synthesis of pharmacologically effective steroids.
The further degradation of 1,4-androstadiene-3,17-dione and 4-androstene-3,17-dione can also be prevented by using mutated microorganisms of the genus Mycobacterium for the fermentative conversion of the sterols (see U.S. Pat. No. 3,684,657). The heretofore grown mutants, however, have the disadvantage that they have an only very limited capability of forming 1,4-androstadiene-3,17-dione or 4-androstene-3,17-dione from sterols.
Accordingly, it is an object of this invention to provide a process for the side chain degradation of sterols which lacks the disadvantages of the conventional methods. This object is met by the process of this invention, which employs specific sterol derivatives in the fermentation with a microorganism culture capable of the side chain degradation of sterols.